Brush holder



Dec. 22, 193

Original Filed May 18, 1928 H D. MUNDAY BRUSH HOLDER 11 Sheets-Sheet l W2 Jv \NVENTOR BY I B MSLAMLH Qw- ATTORNEY.

Dec. 22,. 1931.

H. D. MUNDAY BRUSH HOLDER Original Filed May 18, 1928 11 Sheets-Sheet 2 ML ATTORNEY,

Dec. 22, 1931. H. D. MUNDAY 1,837,827

' BRUSH HOLDER Original .Filed May 18, 1928 l Sheets-Sheet 5 l NVENTOR 15953:? fl Manda;

- M ATTORNEY.

Dec. 22, 1931.

Y H. D. MUNDAY BRUSH HOLDE R Original Filed May 18, 1928 11 Sheets-Sheet 4 k- ATTORNEY.

Dec. 22, 19 31. MUNDAY 1,837,827

BRUSH HOLDER Original Filed May 18, 1928 11 Sheets-Sheet 5 I NVENTOR k. ATTORNEY.

Dec. 22, 1931. MUNDAY 1,837,827

BRUSH HOLDER Original Filed May 18, 1928 11 Sheets-Sheet 6 lNVENTOR florace fi. Manday ATTORNEY Dec. 22, 1931. H. D. MUNDAY 1,837,827

BRUSH HOLDE R Original Filed May 18, 1928 11..,Sheets-Sheet '7 w INVENTOR. Q N 15 mm 211/ Izday m N BY 6 ll Dec. 22, 1931. U D I 1,837,827

BRUSH HOLDER Original Filed May 18, 1928 ll Sheets-Sheet 8 I INVENTOR Q1. ATTORNEY Dec. 22, 1931. H. D. MUNDAY BRUSH HOLDER Original Filed May 1a, 1928 n Sheets-Sheet 9 INVENTOR Horace flflwzaa y BY 5MANHEM.

u. ATTORNEY.

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Dec. 22, 1931. H. D. MUNDAY 1,837,827

BRUSH HOLDER Original Filed May 18, 1928 11 Sheets-Sheet 1o I NVENTOR k1,. ATTORNEY.

Dec. 22, 1931. :0, MUNDAY 1,837,827

BJRUSH HOLDER Original Filed May l8, 1928 ll...Sheets-Sheet ll MATTORNEW.

Patented Dec. 22, 1931 PATENT V OFFEQTE HORACE D. MUNDAY, OF SCHENECTADY, NEW YORK BRUSH HOLDER Application filed May 18, 1928, Serial No.. 278,752. Renewed May 9, 1931. p

This invention relates to current collectors and particularly to brush holders adapted for use with commutators or slip rings.

One object of my invention is to provide a 6 brush holder adapted for use with an abrasive member or with anabrasive brush, wherein the parts are so arranged as to cause the member or brush to exert a truing effect on the commutator of the machine with which 10 it is used.

A further object of the invention is to provide an improved brush holder adapted for use with an abrasive member or an abrasive brush and which willcause the member or I brush, to exerta truing effect on the commutator of the machine with which it is used. A further object ofmy invention is top'rovide a brush holder with means foradvancing or feeding the brush toward the commutator and preventing or resisting any backward motion of the brush. A further object of the invention is to provide a brush holder adapted foruse on a machine which is subject to heavy vibration and wherein the wear onv the moving parts of the brush holder is reduced to a minimum. A further object of my invention is to lessen the rebound of brushes on high speed electric machines, which rebound is apt to occur when slight irregularities exist in the commutator surface.

Sooner or later, from one cause or another, flat spots develop'in many commutators and slip rings. An abrasive cloth and abrasive stones applied by hand are the expedients that are generally tried first to keep the machines in proper working condition. This treatment is generally unsatisfactory and the commutator continues to get worse until finallyfthe machine has to be shut down and the commutator trued by other methods. Small armatures are generally taken out of their frames and the commutator trued in a.

lathe. The commutators of large machines are sometimes trued in place bya portable grinding or turning device. This operation 1s apt to consume several days during. which the machine is out of commission; Undercutting of the mica in=the commutator is one remedy tried for these obvious disadvantages.

mica is not satisfactory because the slots formed in the commutator by the undercutting are apt to fill up with dirt and burn out the armature.

In employing the devices constructed in accordance with the present invention, I overcome the disadvantages just noted. The operation of such devices is automatic and does not require the constant attention of the operator. l urthermore it does not or need not interfere with the normal operation of the machine.

The abrasive or active member employed for truing the commutator may be 'a block formed of pure abrasive and adapted to be employed in a brush holder of the machine or otherwise associated with a brush holder, or the active member may contain conducting material in addition to abrasive material, and such member may function not only as the activetruing element but also as one of the brushes of the machine. I

In the preferred embodiments of my invention means is provided for advancing the abrasive or active member toward the commutator and also for hindering the motion of the abrasive, that is, retardingor preventing motion of the abrasive toward or away from the commutator.

One effect of a hindering means employed by me is to prevent theabrasive from advancing quickly into a low spot of the commutator as the low spot passes under the abrasive and to confine the rubbing of the abrasive to the high spots of the commutator. Or in case the abrasive does enter the low spot of the commutator the hindering means will offer a high resistance to the backward or retrograde motion of the abrasive as the abrasive is being pushed back by the commutator surface onto the high spot. In either of these cases the abrasive will be pressed less against or toward the low spots of the commutator than against other portions of the commutator surface, with the result that ultimately the commutator will be ground to a true cylindrical surface.

The hindering means which I employ may be frictional or it may consist of a viscous .On small commutators undercutting of the i substance such as asphalt interposed between a stationary and movable part of the apparatus. Also, optionally, a sluggishly yielding metal such as lead or solder, may be employed. In certain cases, to provide a hindering of the backward or retrograde movement of the abrasive I may make use of the high resistance offered by a comparatively rigid grinding apparatus when the apparatus is caused to yield structurally a slight amount by the forcing bacl zward of the abrasive by the high spot of the commiiitator. he weight of the grinding apparatus may contribute materially to this effectand if de sired the apparatus may be weighted to increase its inertia.

The means of hindering the motion of the abrasive forms an important feature of the invention, together with the fact that the force for moving the abrasive such that the advancement of the abrasive, radially at least, is harmlessly haltable on contact with the conunutator.

\Vith. a viscous substance interposed to hinder the advancement of the abrasive towards the commutator, permitting the abrasive to move forward only slowly tow: rts the commutator, the abrasive will slowly advance till it strikes the high parts of the revolving COlHlIlllllflllOl. Since the speed of the connnutator is so great in comparison with the slow speed of the abrasive that the abrasive is not able to feed forward into the low spots of the commutator while the commutator is making one revolution, it is evident that the low spots of the commutator will no he touched till all the high spots have been worn down. Consequently the commutator must necessarily become true.

in the use of friction himlering means for truing up a commutator there is the difference that in the case of friction both the nigh part and the low part of the commutator are worn down a the sauna timethe high part being worn down heavily and the low part lightly. In the case of the viscous substance hindering means, as has been seen, the low part of the commutator is not touched at all till the high part has been worn down completely. How friction can be used to true up a commutator can be seen from the fact that the net force causing the advancement of the abrasive is only the excess of the spring or weight over the friction hindering means. On the other hand the total force necessary to cause a retrograde movement of the abrasive equal to the sum of the fric tion and the force of the spring or weight. Consequently the reaction pressure of the commutator on the abrasive will be much greater when the abrasive is being shoved backward from the commutator than when the abrasive is merely stopped in its advance ment towards the con'uuutator. After the high level part of the commutator comes under the abrasive and the abrasive necessarily ceases any further retrograde movement, the slightspring in the apparatus and its supports as a whole may be made to cause the abrasive to continue to exert the maximum pressure on the level high partof the commutator. Consequently, since the abrasive exerts a heavy pressure on the high part of the commutator and a light pressure on the low part of the commutator, the commutator will finally become true.

In forms of the invention described in this application, I employ in my improved truing means a tilting, rocking or canting memher which crmperatcs with the brush or brush-holder to resist or prevent movement of the brush.

Numeroii s objects and advantages of my invention other than those above noted will appear from the following description taken in com'icction iii the accompanying drawings wherein Figure l is a side elevation partly in section of a brush. holder showing a preferred en'ibodiment of my invention;

Figure 2 is a plan view of the structure shown in liigure 1;

Figure 3 a fragn'ientary front view, partly in section, of the structure shown in Figure 1;

Figure l is a perspective view of a detail of the structure shown in Figure 1;

Figure 5 is a side elevation showing a mod ilication;

Figure 6 is a top plan view of the structure shown in Figure 5;

Figures 7 and 8 are views similar respectively to Figures 6 and 5 but showing a modification Figure 9 is a View similar to Figure 8 but showing a further modification;

Figure 10 is a perspective view of part of the structure shown in Figure 9;

Figures ll and 12 are views similar respectively to Figures 9 and 10 but showing a further modification;

Figure 13 is a. side elevation of a brushholder showing a still f rther modification;

Figure 1a is a side elevation of a brushholder showing another modification;

Figure 15 is a plan view of part of the bi'usmholder shown in Figure let;

Figure 1.6 is a perspective view of a supplen'iental part added to convert a. brushholder of the non-positive feeding type into one of the positive feeding type;

Figure 17 is a perspective view of the underside of the structure shown in Figure 16;

Figure 18 is a side elevation of a brushholder showing a further modification;

Figure 19 is a view similar to Figure 18 but showing a still further modification;

Figures 20 and 21 are side elevations, partly in section, showing still other modifications;

Figure 22 is aperspective view, partly in section, of a further modification, in which special means is provided for relieving excessive backward pressure on thebrush;

Figure 23 is a perspective view of part of the structure shown in:Figure 22;

Figure 24 is a plan view of part of the structure shown in Figure 22; v

Figure 25 is a plan view, partly in section, of a modified brush-holder in which re.- lief of the brush or abrasive from excessive commutator pressure comes from the retrograde yielding of the brush-holder box itself when a predetermined maximum brushpressure has been exceeded;

Figure 26 is a side elevation of the structure shown in Figure 25;

Figures 27 and 28 are detail views of parts of the structure shown in Figure 25 Figure 29 is a fragmentary plan view, partly in section, of a modified brush-holder in which relief of the brush or abrasive from excessive commutator pressure comes from the retrograde yielding swivelly of the brushholder box itself when a predetermined maximum brush pressure has been exceeded;

Figure 30 is a side elevation ofthe structure shown in Figure 28; Y

Figure 31 is a side elevation of abrush holder having a positive feed attachment of the toothed type to secure a step-by-step positive advancement of the brush or abrasive;

Figure 32 is a side elevation of a brush holder, showing a further modification;

Figure 33 is a top plan view of the structure shown in Figure 32, and

Figure 34 is a view similar to Figure 32 but showing a still further modification.

Figures 1, 2, 3 and 4 show how an attachment may be added to a standard type of brush holder to convert the latter, without mutilation, into either a positive feed brush holder or into a brush holder. with a hindered motion pressure finger, either type being changed into the other by a simplescrew adjustment.

Referring to Figures 1, 2, 3, and 4, the U- shaped standard or guide 1 is secured bythe pigtail retaining screw 2 through a hole in the horizontal cross-bar of the said U-shaped member 1, to the lug 64 of the brush holder 4. Slidingly mounted on said vertical U-shaped guide 1 is the two-part, L-shaQped, brush-advancing arm 5, engagement of the horizontal bar 6 of said arm being made by the crosshead 7 at the end of said horizontal bar. The sides of the cross-head are made up of the right angle and enlarged ends 8 of the horizontal bar 6, and the L-shaped brackets 9 riveted to said horizontal bar' 6. In the enlarged ends 8 are slots 11 in which are mounted the small screws 12 and 13 vertically adjustable in said slots 11. The twin halves of the arm 5 are connected by the screw 22, on which is the tube 23 ;the thrust of'the brushhead 7 on the vertical guide, and, consequently, the force with which the brush is brought into contact with a flat spot in the commutator. The holes 25a are of body size and are unthreaded.

The friction of the cross-head, that is, the

effect of the binding engagement between the cross-head and the guide in resisting motion in one direction or the other on the guide, may be varied by varying its effective length, the effective length depending on theposition of lie-screws 12 and 13 in the slot 11. In varying the position of the screws 12 and 13 to vary the effective length of the cross-head 7, in order to vary the friction, the position of the upper screw 12 has an effect when the arm 5 is canted clockwise; and the position of the lower screw 13 has an effect when the arm is canted counter-clockwise. In a clockwise cant, corner 33 and the head of screw 12 are the friction, or bearing points, the vertical distance between them being the effective length of the cross-head 7. In a counter-clockwise cant, corner 54 and the head of screw 13 are the friction, or hearing points.

, It is obvious that if only one force, such as the reactive thrust of thebrush 35, acts upwards on the arm 5, the cant will be counterclockwise. Itis obvious also that if only one force, such as the pressure finger 24, acts downwards on the arm5, the cant will be clockwise. If, however, both the pressure finger and the brush act on the arm 5 at the same time, the cant is reversed, being now counter-clockwise instead of clockwise as in the case just mentioned. Consequently, if we wish to vary the friction. of the cross-head 7 when the arm 5 is in engagement with the brush 35, screw 13 should be adjusted in the slot 11, keeping it, however, below the level of the corner 54. "If it is'desired to lock the arm 5 on the upper part of the guide 1 to get the arm 5 out of the way of the brush-holder box 36 in order to insert a new brush or ab.- rasive member, the friction on the cross-head may be increased by lowering. screw 12, keepingit, however, above the level of the corner Between the extremities of the limbs of the U-shaped guide 1 is mounted a pair of concentric cylinders 41 and 42 with a coating of asphalt 43 between them; the inner one 42 slightly the longer, fitting accurately but freely between said extremities, is clamped thereto by the screw 44. To the outer cylinder is clamped by the screw 45 the lever 46 swivelly connected by the'pin 47 to the connecting rod 48, the latter being swivelly connected by the pin 49 to the brush-advancing arm Riveted to the feet 50 of the brushadvancing arm 5 are the thin phosphor bronze spring 50a and cross-bar 50?), a shoe 5300 being riveted to the spring 50a. The thumb-screw 51, threaded into the cross-bar 50b and secured by the thumb-hart may be adjusted to limit or annui the action oi the spring 50a.

The pigtail retaining screw 2 is set up against a stilt lock Washer 56, but not quite to the limit. Under an excessive reaction thrust of the brush 35, the lock Washer can be compressed slightly, thus permitting the U-shaped guide 1 to be tilted slightly to the left, thus giving relief to the excessive reaction thrust.

The sides and top of the brush or active member 35 may be smeared with a coating of some sticky or pasty substance 59, such as cylinder oil and graphite mixed to a pasty consistency. This has tendency to stop the chatter of the active member when a pure abrasive, and when the commutator is running against the acute angle ot the abrasive.

This pasty filler 59 may delay the movement of the brush or abrasive; consequently the asphalt 13 may in certain cases be omitted or thrown out of action, and yet we can get delayed action from the pasty filler alone.

In the operation of this brush holder the asphalt hindering means may be thrown out of action by backing oil slightly screw 14; or screw 15 may be h cked ott, or one of the pins 17 or 4:9 removed.

To advance the active member positively, screw 13 is raised till the effective length of the cross-head becomes so short that the reactive thrust of the brush cramps the crosshead on the guide 1 and prevents the crosshead from sliding upwards on the guide 1.

How hard the brush or abrasive member is brought into contact with the low spot or" the commutator depends on the position of the screw 22 in one of the holes 25a; with the screw 22 in the left hole, as shown in the drawings, the contact pressure is least; with screw 22 in the right hole the contact pres sure is greatest.

When it is desired to Operate non-positively the screw 13 is lowered till the reactive thrust of the brush or active member will not cramp or lock the cross-head on the guide 1.

To avoid any possibility of the cross-head cramping and stopping on a downward in ovement, the screw 12 may be kept in its highest position; although there is small possibility of this happening if the brush-advancing arm 5 is in contact with the brush or abrasive member at the start of operations.

here there is no abrupt jump from the low to the high part of the commutator, the delayed action hindering means may be omitted; when, however, there is an abrupt jump it is generally preferable to use some form of delayed action hindering means, such as the asphalt hindering means.

here the low part of the commutator is not very deep, or within the limits of the inherent structural yielding of the device, a positive feed may be used; in this way we can get a heavy pressure on the high parts of the commutator and a rapid cutting down of the same. Where the fiat spot of the com mutator is deep or greater than the inherent structural yielding of the device the positive feed may be omitted; however, reliet means in the form of the stiii lock washer provided so that a positive teed may be used even where the low spot is deep. But a positive feed with delaying means may be used to true a deep flat spot without reliet means.

Relief means are also provided by a retrograde movement of the box itself, independent of the rest of the brush-holder body. A dovetail tongue 61 in the shank 3 engages a complementary dovetail groove 62 in the rear wall of the box 36. A lug (Sa integral with box 36 supports the feeding attachment, and is strongly heid against shank 3 by spring 65 stressed by cap-screw 66 threaded into shank 23, said spring being compressed under an excessive brush thrust.

The purpose of the phosphor bronze spring 50 to give a quick follow up to the brush independent of the movement of the other parts of the zu'iparatus, as in the case o't' high speed machines with slight irregularities in the commutator. The screw filmay be adjusted to limit. the rel'xound oi' the brush in this case to any amount desired. Vhere an abrasive brush is being advanced under the control of delayed action hindering means and it is desired not to lose the current carrying capacity of even one brush (as where there are only two or four or a few brushes on a commutator) this phosphor bronze spring will serve to keep the brush in contact with the low spots of the commutator as well as the high parts. here it is desired to hurdle the flat spots of the commutator the thumb-screw 51 is advanced till it makes contact with the spring 500 in its unsprung position. The spring 50a is preterably comparatively weakthat is. in comparison with the spring actuating the brush-holder pressure linger 2 1.

It is evident from the above explanation that by a simple adjustment of scrc a brush holder of a common type may be converted ilno a positive teed brush holder with only a nominal amount of friction to hinder the ad vanccmeut ot the brush or abrasive into the tint spot ot the commutator; or this friction. instead of being nominal, may be regulated to be of substantial amount; or the movement may be hindered by delaying means, such a viscous substance like asphalt or other siuggishly yielding substance. The asphalt can be easily made to hinder in the forward direction only, as by the simple substitution of a stranded wire or chain for the connectingrod48.

Or the effectivelength of the cross-head may be adjustedto avoid the positivefeed; in this case we may have friction hindering means with orwithout asphalt :hindering means. Both the friction to hinder a forward movement andv tohinder a retrograde movement are independently adjustable. The asphalt hindering means may be used alone, the friction being'regulated to be merely nominal. 1 f i Instead of a pasty fillermade up of cylinder oil and graphite, variousother powdery substances may be used tomix with the cylinder oil; some of these are whiting, powdered chalk, clay, carbon powder. Instead "of cylinder oil, other oilsor greases may be used to mix with thesolid substances; some of these are Vaseline, glycerine and .castor oil. Other substances in their commercial form are adapted to act as a filler between the brush or abrasive and the brush-holder box and cause a sluggish movement of the'brush or abrasive; the solid belt dressing in common use is one of these; another is modeling clay. This modeling cla is made up of clay and glycerine; more gl ycerine may beadded to make it less doughy and more pasty. Cylinder oil may be mixed with asphalt to reduce its viscosity to any amount desired. The sticky substance used onsticky fly-paper may be used as delayed action hindering means; this is made of resin and castoroil.

Instead of using a-pasty filler to prevent chattering of the abrasive member, a form of construction may be given the abrasive member that will tend to stop chattering. Such a form as is described in a copending application Serial Number 278,751 filed May 18, 1929, an abrasive member. with a wedgeshaped endv coacting with a pusher member witha similar wedge-shaped endgvill tend to stop chattering of the abrasive member or abrasive brush.- V

In the modification shown" in Figures 5 and 6 a U-shaped guide 61is secured by the screw 62- to the brush-holder shank 63. Slidably mounted in this U-shaped guide is the inverted L-shaped, brush-engaging" member 64 made up oftwo similar L-shaped members 65, which'are integrally unitedto form a unit .by the contacttip 66 at the lower end of. the vertical member, and the rivet 67 and I spacin'gbushing 68 near the middleof the horizontal portionof the L-shapedmember 64. The pressure finger 69 exerts its thrust on the spacing bushing 68. The bent ends 70 and the riveted blocks 71 form. the sides of a groove to coact with the limbs of the guidex61.

In the operation of this attachment for truing a commutator an abrasive brush 72 or abrasive block is substituted for the usual brush. It is evident that when the member 64 is advancing there can be no binding of this member on the guide 61. When a backward thrust of the brush comes because of a high spot of the commutator coming under the brush the member 64 instantly locks on the guide 61 without any slight retrograde movement while lost motion or backlash is being taken up. It is evident that if the width of the horizontal parts 65 of the L- shaped member is great enough to not lock, then we have a friction finger brush holder instead of a positive feed brush holder.

In the modification shown in Figures 7 and 8 there is formed in the brush-holder body a guide 81 located between the brush-holder box 82 and the brush-holder shank 83. Slidably disposed in this guide is the longer limb 84 of a U-shaped brush-engaging member 85, the shorter limb 86 of which makes contact with the brush 87 at 88. To the end of this longer limb 84 is attached by the rivets 89 a spacing member 8911, the purpose of which is to permit only a portion of the limb 84 to come in contact with the sides of the groove 81. The spacing member 89'a'can be easily removed and a wider or narrower one substituted. The narrower this one is, the greater is the tendency of the limb 84 to bind in the groove 81 when the U-shaped member is subjected to an offset thrust, such as is received at 88 from the reaction pressure of the brush 87. The thrust of the brush-holder pressure finger comes at 90 between the limbs 84 and 86, thus advancing the longer limb 84 as far as possible in'the guide 81 and effectively avoiding any manifestation of backlash or lost motion when a high spot of ,the commutator comes under the brush 87 and shoves it backwards. What yielding there is in this case will have to come from the structural yielding of the brush holder and its supporting partsthe brush-holder stud and brush-holder yoke.

When it is desired to use the brush holder in the usual way, the U-shaped member is pulled out of the groove without the necessity of removing the screw or nuts or other means of attachment to the brush holder body. 7 If the spacing member 89a is too wide to lock under the reaction thrust of the brush, the result is the equivalent of a friction finger, or rather the equivalent of a friction finger brush-holder.

In the modification shown in Figures 9 and 10 a box guide 91, two sides of which are 92 and 93, is attached by the screw 94 to the front wall 95 of the brush-holder box 96. In the inner side 92 of the guide 91 is the hole 97 large enough to permit to project, therethrough'the protuberance 98, threaded for the usual purpose of receiving the brush pigtail retaining screw, for which has been substituted the longer screw 94. The/inverted side that slidably engages the box guide 91 divided into two parts 100; this division is for the purpose of straddling the screw 9 1 and protuberance 98. The blocks 101 riveted to the parts 100 determine the binding or pinching limits of the parts 100 in the guide 91.

The vertical width of the block 101 determines whether this type of brush holder is a positive feed brush holder or the equivalent of a friction finger brush holder. It is the former when the blocks are narrow enough to cause locking under the reaction thrust of the brush: and the latter when the blocks are too wide to cause locking.

1n the modification shown in Figures 11. and 12 there is a circumferentially grooved or collared bushing 102 secured to the front side of the brush-holder box 103 by the capscrew 10-1 substituted for the brush-holder pigtail retaining screw. To brace the structure there is provided the fiat strap 105 and the thumb-screw 106. All spring or yielding is taken up by snugly setting up the thumbscrew 100, which is then secured by the knurled jam-nut 107. The brush-engaging U-shaped member 108 has the longer side divided into two limbs 109, 109 which are mounted astride the bushing 102 and in the groove 110 thereof. The said brush-engaging member 108 is forwardly actuated by the springs 110a and screws 110?), the springs 110a being put under tension by the knurled thumb-nuts 1100. The positive advancement of the member arises from the fact that the reaction offset thrust of the brush 110d is so far to the side of the limbs 109, 109 that they bind or pinch in the groove 110 when the member 108 is shoved backwards by the brush. There is no locking of the member 108 when moving forward, because the screw 110?) is not oil'set far enough from the limbs to cause the latter to lock in the groove 110.

It is evident that by changing the proportion of the parts, such as by decreasing the distance between the sides of the U-shaped member or by increasing the diameter of the groove, we can get the equivalent of afriction finger brush holder.

In the modification shown in Figure 13 the pressure finger 121 is slidabiy mounted on the stud 122, the right-hand end of said pressure finger being expanded into a cylindrical cross-head 123 which slides freely on the said stud. The reduced end 1241 of this stud, together with the nut 125, serve to close the clamp 126 which clamps the brushholder shank 127 to the brush-holder stud 128. iiveted to the reduced upper end of the stud 122 is the spring holder 129 housing the flat spring 130, the outer end 131 of which makes contact with the pressure finger 121 in the shallow trough 132 on the top side of said pressure finger. The disposal of the end of the spring 130 in the trough of the pressure finger serves to keep the said pressure finger in alignment with the axis of the brush-holder box 123. Additional security as to alignment may be had by means of the keyway 134 in the stud 122, into which keyway projects the end of the screw 135 held securely in the cross-head 123 by the jam-nut 1341. For the purpose of regulating or annuling the action of the auxiliary spring 137 there is mounted in the outer end of the pressure finger 121 the screw 138 secured by the knurled thumb-nut 139. This screw 139 is in line with the center of the brush-engaging hammer 140 riveted to the end of the auxiliary spring 137. The set-screw 1 11 serves to keep the stud 122 in position when the nut 125 is backed off.

l Vhen the pressure finger 121 is resisting an upward thrust of the brush 1412 the crosshead 123 makes contact with the stud 122 at the points a and 5. Through these points are drawn the construction line a0 and 60, making an angle (,6 with a normal to the stud 122, the angle being the angle whose tangent is equal to the coefficient of friction. This angle is taken as 15 degrees corresponding to a coeflicient of friction of something less than 27/100. If the reaction thrust of the brush is to the left of a vertical line through the point of intersection 0 there will be no slipping of the pressure finger on the stud 122; if the reaction thrust of the brush is to the right of the point 0 the pressure finger will slip on the stud, but with frictional re sistance. WVith the former construction we have a positive feed brush holder; in the latter construction a friction finger brush holder. The point of contact 0 of the spring 139 with the pressure finger should preferably be to the right of the point 0. Near the top of the stud 122 is the groove 1 13 adapted to receive the end of the screw 135 thereby permitting swiveling of the pressure finger 121 on the stud 142 when the pressure finger is raised to its maximum position. In this way anew brush can be inserted in the brushholder box 135.

\Vhen this brush holder is used in the usual way the screw 138 is backed off widely or removed, thus permitting unimpeded play to the auxiliary spring 137 If the brush holder is used with high-speed electric machines to prevent the rebound of the brush from commutators with slight flat spots in them the desired tension is first put on the main spring 30 by adjustment of the arm 1 14 in the notches 145. The screw 138 is then advanced to contact or nearly to contact with the brushengaging hammer 1 10. hen the brush hold er is used to true up a commutator, an abra sive brush or an abrasive block is substituted for the usual brush; then, with a slight stress on the auxiliary spring 139 the screw 138 is advanced to contact with the brushengaging hammer 140; finally the proper stress is put on the main spring 130. To permit a slight retrograde movement of the brush when a high spot of the commutator comes under the brush, dependence is made on a slight structural yielding of the various parts-the pressure finger, the stud 122,the clamps 126, the brush-holder stud 128 and the brush-holder yoke.

In Figures 14, 15, 16 and'17 is shown a brushholder substantially of a form now in use, and the means added to adapt it to advance the brush positively. The brush-holder shank is in the form of a vertical stem 191 integral with the brush-holder box 192 at its lower end; By, means of the clamping members 193 and the square-headed bolts 194 vertically adjustable in the slot 195 in the stem 191 the brush holder is secured to the brushholder stud 196. A U-shaped wedge-shaped sheet metal catch 197 serves to adjustthe tension of the brush-actuating spring 198.

The catch holds its position through the engagement of the edge 199 of the horizontal part'of the catch with the teeth 200 of the stem, and the engagement of the nibs 201 in its lower part with the ribs 2020f the stem 191. The lower end of the spring 198 is secured to the rod 203, the lower end 204 of which rod engages the brush 205 in the hole 206; in this way the alignment of the spring is preserved.

The added part that adapts this old type of,

brush holder for positive feeding is the friction or chocking cap 207, shown separately in the two perspective views in Figures 16 and 17. This friction cap 207 is intended to slide on the stem 191 and for this: purpose has projecting from the main part two L- shaped lugs 208 the free limbs of which slidably engage the grooves 209 in the stein 191, the sides 210 and210a of the limbs of the L- shaped lugs making contact with the sides of the groove 209. If there is friction or binding by the lugs against the sides of the grooves whenthe cap 207 is moving downwards under the action of the spring 198 the pressure comes on the lines a and b. The vertical distance between a and b is preferably. made so great that the friction will not be great enough to stop the forward motion of the cap 207. On a retrograde movement of the cap 207 under the reaction thrust of the brush 205, the. pressure on the lugs 208 comes at the lines 0 and d. The vertical distance between .0 and d isso small that the lugs bind in the groove when the cap receives a reaction thrust of the brush at the point 211. Since the thrust of the spring 198 is received at a point 211a on the cap between its point of engagement 211 with the brush and its contact point with the groove 209 there is nobacklash to be taken up and preventinstant checking of the cap under the reaction thrust of thebrush as a highspot of the commutator 212 comes under the brush. A cotter pin 213 in the groove at the upper end of the stem serves to keep the 7 parts assembled. a In truing a. commutator by:this. type of positive feed brush an abrasive brush or or by using a fibre bushing on the brush- 7 holder stud 196.

In Figure 18 is shown how a brush holder of a type in common use has been modified to adapt it to positive feeding. The ordinary brush-holder finger is removed, and a spiral spring 215 with a longer arm 216 substituted for the usual spring. A short vertical tube 217 is secured to the brush-holder shank 218 by the cap-screw 219. On this vertical tube is splined the pressure finger 220, the expanded tubular end 221 of said pressure finger engaging the vertical tube 217 and key 222, which key restrains the pressure finger to a vertical movement till the extreme upward position of the pressure finger has been reached, when it passes out of engagement with the key 222 and is then free to swivel on the vertical tube 217 to permit the easy insertion of a brush.

7 Figure 19 shows the means of adapting one of the earlier types of brush holders to positive feeding. In this type of brush holder the spring 241 is slotted from about the point 242 to the end of the spring. Positioned in this slot is the square rod 243 rigidly attached to the brush-holder shank 244 by the clamp 245 and screws 246. Slidably mounted on the square rod 243 by means of the square hole. 247 near its end is the brush-engaging horizontal bar 248 making contact near its outer end with the brush or abrasive member 249 bearing on the commutator 250. The spring 241 acts on the bar 248 through the spacing block 251 adjustably secured by the. screw 252 in one of several holes 253.

a bit, friction will be increased on account of the greater leverage thus given to the bracket 271; on the other hand, friction will be reduced if the step 274- is cut away a bit, because the leverage in this case will not be so great.

In the modification shown in Figure 21 the upper part of one of the edges of the brush is reduced slightly in step "fashion as is the brush in Figure 20. Formed integral with the rest 275 and extending laterally therefrom is the rectangular Z-shaped strap 276 ending in a nib 277 which loosely enters a small, square hole 278 in the vertical leg 270 of the inverted L-shaped bracket 280 the end of the nib 277 being peened over in order to secure the bracket 280 in loosely swivclling assemblage with the brush 281.

in Figures 2 and is shown another nmdilication ot the positive feed brush holder which differs from most forms previously described in respect to relief means for permitting a retrograde movement of the brush when a. certain mafiimum pressure has been exceeded. In certain of the positive feed brush holders previously described the relief spring permitted retrograde movement to the brush when a certain pressure has been exceeded, but not to the brush holder; in this modification both the brush and the brush holder move backwards when a certain pressure is exceeded, thus doing away with the possibility of wear oi. the brush and. the brush h older.

In the brush holder shown in Figures 522, 23

nd 2d the hexagonal ln'uslrholder stud 301 is secured to the machine frame in acertain definite position in relation to the hexagonal faces at the stud. hitting on said stud and insulated from it by a hexagonal libre tube, the thiclv. metal sleeve 302 secured to said hexagonal stud by the cap-screw 303 and jam-nut 30s. To the thiclr sleeve 302 is z-ilidingly secured by the cap-screws 305 and the flat bar 306 the brush-holder set 307, consisting of tour brush. holders integrally united to themselves and to the tongue 308.

In the shanl: 309 of each brush holder is formed a narrow compartment or groove 310 with its side walls on both sides partly cut away in the middle part to permit passage of the brush-holder pressure linger 311. Mounted in this groove by its step-like expanded end 312 is the brush-engaging square rod or auxiliary pressure finger 313 forwardly actuated to advance the brush by the pressure finger spring 3l1 which also serves as a pressure linger, the pressure linger being merely the free end of the flat spring 311.

In the tongue 308 are elongated holes 2 13a by which vertical adjustment is made to fit commutator-s of ditlerent dian'icters when the brush holder is used in the usual way without the truing device. hen the truing attachment is used and where there may be more retrograde movement of the brush or abrasive (if an abrasive block has been substituted for the brush) than can be taken care of by the mere structural yielding of the brush holder and supporting parts, provision is made for a verti *al reliei movement the tongue 308 by not setting up the capscrews 305 quite tight; or by setting them up against a collar or spacing member that will allow a slight clearance between the tongue and the ilat face of the thick sleeve 302. For advancing the brush holder towards the commutator there are straps 314 bearing against be top of the tongue 308, the stilt flat spring oil to advance the said straps 314 and jamnuts 315 on the studs 316 to stress the spring 317. llhe strap 3H is loosely secured at the lower end by the jam-nut 30a which has a reduced portion 318 oi cylindrical form that ac elongated hole 319 in strap 31 i and en permits said strap to swivel to some extent. To limit the forward movement of the brush holder towards the commutator there is a -screw 320 threaded into the top of the l: sleeve 302- and positioned under the projecting horizontally from the ".e 303, the striking of the under side E f said lug on the head of cap-screw 320 serving to limit the advancement of the brush holder.

la the operation of this brush holder without the positive teed attachn'ient in use the relief means never comes into action; and in that case the 'ap-screws 305 may be set up tight clamping the t ngue 308 to the thick sleeve 302.

lvhcn the positive feed attachment in use whether with a brush c(mtainin; g' say 25% abrasive, or with an abrasive block, the tongue moves vertically against the stress of the spring 317 to prevent any possibility of injury to the brush holder when any ahnormal pressure comes on the brush or abrasive block that can not be taken care of by the structural yielding ol" the brush holder and supporting structure. Such abnormal pressure might arise from a deep llat spot in the connnutator or from a worn bearing permitting a vertical movement of the armature from sudden starting of the motor or from a rough track (when the brush holder is used on a street-car motor).

In addition to the advantage in using the positive teed attaclnnent to true a commutator there is a further advantage in using the positive feed attachment with the ordinary brush on the brush llOlhGlS ol streetcar motors where there is no intention to true a conn'nutator. In street-car motors there is a great deal of wear of the brushes because the sand and grit of the street get in between the brush and the sides of the brush holder box: thus causing a grinding action between the brush and the sides of the box, resulting in much wear of the brush and the sides of the box. This grinding action is the result of theslightto-and-fro movement of the brush holder in the box. It is evident that with a positive feed attachment in use that this to-and-fro movement is eliminated, all retrograde movements of the brush being accompanied by an equal retrograde movement of the brush holder as well. Consequently the wear of the brush and box due to the sand and grit is eliminated. It is evident that the groove 310 maybe adjacent to the brush-holder box, in which case ,they will have a common wall. 7

In modifications shown in Figures to 28 the movement of the brush-holder box and its integral or accessory parts is due to the brush-holder box and integral parts forming one of the movable sides of a parallelogram-of-motion arrangement, the other two movable sides being two pairs of comparatively flat springs, which arestifl in comparison with the actuating spring of the brush-holder pressure finger.

On the square brush-holder stud 355. with a fibre tube telescoping. and insulating it there is secured the square metal sleeve 356 to which are attached the fixed ends of the four fiat springs 357, the other ends of said springs being attached to the movable guide 358 to which is adjustably secured by the cap-bolts 359 the tongue 360 integral with the brush-holder box .361. It is evident that when a certain maximum brush pressure has been exceeded the said springs 357 will bend and allow a retrograde movement of the brush holder box 361. For the purpose of truing commutators most efliciently in combination with a positive feed attachment, it is desirable that these springs 357 be assembled in such a way that they have a strong downward stress. uch a downward stress may be secured by giving the springsbefore assemblage an initial fiexure as shown-in Figures 27 and 28 for the upper and lower springs respectively. By properly choosin the springs the relief movement of the brus holder willtake place before it is damaged or before any shearing action of the commutator on the brush or abrasive occurs. It is evident that instead of springs connecting links and pivots could be used to get a motion of the brush holder parallel to its initial position. The-reason for having four springs instead of two is to diminish theeffeet that the breaking of one spring will have v on the functioning of the brush holder.

Referring toFigures 29 and 30, onv the rounded-cornered square brush-holder stud 371 telescoped and insulated by a fibre tube, is mounted the thick sleeve 372 turned down at either end to form a spindle 373, on which swivels,by means of the split bearing clamp 374-374a, the guide 375 in which is mounted adjustable by the cap-bolts 376, the tongue 376a integrally united to the brush-holder boxes .37 7. To give aconstant thrust of the brush-holder towards the commutator there is the' stifl spiral spring 378 stressed between the lug 379 projecting from the clamp 374a and" the square bar 380 attached to thesleeve 372. By means of the nut 381 on the capbolt 382 any desired stress can be'secured on spring 8. The forward motion of the brush holder is stopped by the clamp 374 coming in contact with the ends of the square bar 380. Clamps 374a and guide 375 are integral.

One. objection to the swivel type of relief means is that a retrograde movement of the brush holder tends to tip the brush slightly on the commutator.

Referring to Figure 31, to the shank 391of the brush holder 392 is clamped by the clamp 393 and screws 394' the vertical snubber bar 395 of rectangular section and notched on the right-hand face with teeth396 like those in a fine file, the formation of the teeth being such that a downward motion of the snubber bar (if it were used as a file) would correspond to the cutting stroke of the ordinary'fine file.

On the snubber bar 395 is slidingly mounted the auxiliary pressure finger 397. By cutting away one side of thesquare hole in the a auxiliary pressure finger 397, as indicated by the dotted line 398, a chisel edge 399 is secured in the auxiliary pressure finger to engage the teeth 396. If there are fifty teeth to the inch 7 it is evident that the greatest retrograde movement of the brush or abrasive can amount to no more than 2/100 of an inch; and the average retrograde movement is of course much less than this. The teeth may attached to the snubber bar by screws; or the teeth may be cut in soft steel snubber bar, which is then case-hardened, the tooth-engagformed in a separate piece like a nail file and i ing part of the auxiliary pressure finger being preferably also case-hardened. I It; is evident that without any teeth on the snubber bar 398, said snubber bar being left soft and the engaging edge 399 of the auxiliary pressure finger case-hardened, the hardened edge 1 399 will tend to dig into the snubber bar and prevent any retrograde movement of the brush or abrasive. I

It is evident also that the variation of hardened teeth in the snubber bar in engagement" with a soft auxiliary pressure finger will be likewise operative.

In the modification shown in Figures 32 and 33 a brush holder of a type in common use is adapted for truing acommutator by 

